in reply to (jeffa) Re: Closures as Itterators
in thread Closures as Itterators

I've read elsewhere about subtleties with the instantiation syntax I used (I think it was on a python propaganda page) Easy enough to change.

The loop construct, however, is a bit strained. I don't really want to clobber $_, but I do like: 

while(chomp($row = <$fh>)) {

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Much better than: 
while(1) {
   chomp($row = <$fh>) or last;

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I have Damians book, but only made it about half way through before losing the thread. I don't do much OO programming, so I didn't have many concrete examples to toy with while reading the book. It was very well written though, got much further than any other OO book I've tried.

-Blake

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Re: Re: (jeffa) Re: Closures as Itterators
by dragonchild (Archbishop) on Jul 02, 2001 at 21:33 UTC
    To avoid clobbering $_, it's quite easy to just do something like: 

    sub thingy {
    # blah blah blah...
    local $_;
    while (<$fh>) {
        chomp;
        # do stuff here...
    }
    # more stuff here...
}

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    In fact, I do that with every package function I write, even if I don't intend on using $_ explitly, because I don't want to depend on a built-in function not clobbering $_ for me in an attempt to be helpful.

    Furthermore, the while(chomp($row=<$fh>)) syntax is very dangerous. It will miss the last line of a file, if that line doesn't end with a newline. The while() loop is dependent on the return of something from chomp, not the definedness of $row. I would definitely use something like: 

    while (defined(my $row = <$fh>)) {
    chomp $row;
    # stuff here...
}

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[d/l]
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      I know what while(chomp($row = <$fh>)) is doing. In this case, though, I'm reading from a very specific data file (which does end with a newline) and the very nature of the routine prevents it from using the last line of the data file 99.9% of the time anyway. (is is primarily used to grab a few lines from the middle of the file)
      Thanks for the $_ tip, though, I like it.

      -Blake

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[d/l]
        I know what while(chomp($row = <$fh>)) is doing. In this case, though, I'm reading from a very specific data file ...

        If I had a nickel for every time I heard someone say something like that, PM would never have to beg for money. The issue isn't whether or not your specific data file at this specific instance will or will not break your syntax. The issue is whether or not that syntax is the better way to write it. Why introduce a potential bug into your code?

        Now, your reply is that you know where the issue is and you won't make that mistake when it matters.

        My reply to that is simple - why get into a bad habit? Always code with good habits. My swim coach in 3rd grade was never happy with "Practice makes perfect" ... he believe in "Perfect practice makes perfect". I hated him at the time, but I thank him now.

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